Deuteronomy 3:21

And I commanded Joshua at that time, saying, Thine eyes have seen all that the Lord, your God, hath done unto these two kings; so shall the Lord do unto all the kingdoms whither thou passest. The conquered lands of the vanquished kings were lying before Joshua's eight, and this fact gave Joshua a perpetual guarantee of the Lord's assistance in the work which was still before him, which he must do after the death of Moses.